1. EP375 Computational Physics
Topic 14
VIDEO PROCESSING
Department of Engineering Physics
University of Gaziantep
Apr 2016

2. Content Example Applications Functions to be used: VideoReader()
rgb2gray()
im2bw()
imshow()
regionprops()

3. Introduction We have seen 2D or 3D plots of basic data.
In this chapter we will discus some of the elementary processes that can be applied to images.

4. % vp0.m
% frames to movie
% get 1.bmp, 2.bmp and 3.bmp from course web page %
clear; clc;
count = 0; Nframe = 3; Dframe = 5;
mov = avifile('example.avi','compression','None');
for i=1:Nframe
name = strcat(num2str(i),'.bmp');
v = imread(name);
while count<Dframe
count = count + 1;
imshow(v);
F = getframe(gca);
mov = addframe(mov, F);
end
count = 0;
mov = close(mov);

5. % vp1.m
% reading video info
clc; clear
v = VideoReader('laser.avi');
t = v.Duration
fr = v.FrameRate
nFrame = uint32(t * fr)
v1 = read(v,30); % get 30th frame
imshow(v1) % diplay

6. % vp2.m
% reading video info
clc; clear
v = VideoReader(‘freefall.avi');
t = v.Duration
fr = v.FrameRate
nFrame = uint32(t * fr)
for i=1:nFrame
v1 = read(v,i); % get ith frame
imshow(v1) % diplay
end

8. % vp3.m
% reading video
clc; clear
%v = VideoReader('laser.avi');
v = VideoReader(‘fallingball3.avi');
t = v.Duration;
fr = v.FrameRate;
nFrame = uint32(t * fr);
for i=1:nFrame
A = read(v, i); % get ith frame
B = rgb2gray(A); % convert to gray scale
C = B>175; % convert to black-white
subplot(2,2,1); imshow(A)
subplot(2,2,2); imshow(B);
subplot(2,2,3); imshow(C)
pause(1/fr);
end

9. % vp4.m
% ccd
clc; clear
v = VideoReader('laser.avi');
t = v.Duration;
fr = v.FrameRate;
nFrame = uint32(t * fr);
v1 = rgb2gray(read(v,1)); % get 1st frame
v3 = rgb2gray(read(v,1)); % get 1st frame
for i=2:nFrame
v2 = rgb2gray(read(v,i));
v3 = v3 + imabsdiff(v1,v2);
imshow(v3)
end

10. % vp5.m
% circles
a = imread('circles.png');
g = rgb2gray(a);
bw = g > 100;
imshow(bw)
stats = regionprops('table',bw,'Centroid',...
'MajorAxisLength','MinorAxisLength')
centers = stats.Centroid;
diameters = mean([stats.MajorAxisLength ...
stats.MinorAxisLength],2);
radii = diameters/2;
hold on
viscircles(centers,radii);
hold off

11. % vp6.m
% tracker
clear; clc;
v = VideoReader('laser.mp4');
t = v.Duration;
fr = v.FrameRate;
nFrame = uint16(t * fr);
newvid = VideoWriter('newfile');
newvid.FrameRate=8;
open(newvid)
for k = 50:200
v1 = read(v,k);
imshow(v1)
v2 = im2bw(v1,0.8);
stat = regionprops(v2);
[w, h] = size(stat);
if size(stat) > 0
rectangle('Position', stat(1).BoundingBox, 'EdgeColor', 'b');
cX = stat(1).Centroid(1);
cY = stat(1).Centroid(2);
fprintf('%d %d\n',cX,cY);
end
frame = getframe;
writeVideo(newvid,frame);
close(newvid)

12. % vp7.m
% measurement of gravitational acceleration from video
clear; clc;
v = VideoReader('fallingball7.avi');
nFrame = uint16(v.Duuration * v.FrameRate);
v1 = read(v,1); % get first frame
for k = 2:nFrame
v2 = read(v,k);
v3 = imabsdiff(v1,v2);
v4 = im2bw(v3,0.2);
imshow(v4);
stat = regionprops(v4);
if size(stat) > 0
rectangle('Position', stat(1).BoundingBox,'EdgeColor', 'g');
cX = stat(1).Centroid(1);
cY = stat(1).Centroid(2);
fprintf('%d -> %d %d\n',k,cX,cY);
T(k) = double(k)/fr;
y(k) = cY;
end
frame = getframe;
% size of ping ball is 42mm which corresponds 15px in the video
t = T(2:end);
y = (v.Height-y(2:end)) * 42e-3/15;
plot(t,y,'*')

13. References:
[1]. Numerical Methods for Engineers, 6th Ed. S.C. Chapra, Mc Graw Hill (2010)
[2].
[3]. Numerical Methods in Engineering with MATLAB, J. Kiusalaas, Cambridge University Press (2005)
[4]. Essential MATLAB for Engineers and Scientist, 3rd Ed Hahn B., Valentine D.T. (2007)
[5]. Computational Physics,
Giordano J.N. Prentice Hall (1997)